I was cruising through a few of the older posts from back in the early days (or what I think might have been the early days) when I stumbled upon an interesting site, http://www.jstor.org. I forgot who originally discovered it, but I feel this site has an enormous amount of information regarding the history of the sling. When doing a search, type in sling and click the Archaeology box. The highest scoring articles are absolutely amazing, for me anyways. I hope this helps the cause. Keep it going.

PS- there are other articles regarding sling range compared to the bow and such under other categories.